In recent years, many vehicle control systems have been developed to enhance vehicle stability and tracking performance in critical dynamic situations. Such vehicle control systems include yaw stability control (YSC) systems, roll stability control (RSC) systems, integrated vehicle dynamic control systems, and others. In these systems, knowledge of the vehicle roll and pitch attitude is very important. For example, in yaw stability control systems, the effect of vehicle body roll and pitch, as well as the dynamically changing road super-elevations and road grades, is significant because it directly influences both the vehicle lateral dynamics and lateral acceleration measurements. In roll stability control systems, roll angle is one of the most important variables used to construct feedback pressure command and combat the detected roll instability. Hence, a successful vehicle dynamics control must involve an accurate determination of the vehicle roll and pitch attitude. However, values of roll and pitch are not directly measured on production vehicles and therefore must be estimated instead.
When actively controlling a vehicle's motion using systems such as the braking system, it is important to accurately estimate the state and attitudes of the vehicle. Achieving an accurate sideslip estimate will provide the opportunity to control the vehicle's sideslip to an appropriate value. To those familiar with the art, it is known that sideslip is difficult to determine using inertial sensors due mainly to integration drift, which is caused by sensor offset and contamination of the lateral acceleration signal by gravity. To accurately account for the acceleration due to gravity, it is necessary to know the global roll angle. A roll rate sensor alone can give you an indication of global roll angle, but due to offsets in the roll rate sensor and inaccuracy in the pitch estimate, the error in the global roll angle can quickly accumulate. Therefore, it would be desirable to control this accumulation of error.